The present invention generally relates to endoprosthesis devices and to a method for making same. More particularly, the invention relates to a generally tubular endoprosthesis that includes a pyrolytic amorphous carbon layer The carbon-layered surface of the endoprosthesis presents an antithrombogenic interface with the tissue within which it is implanted. This interface renders the endoprosthesis less thrombogenic and can be useful in restraining the endoprosthesis in the event of its fracture while implanted. The carbon layer itself also protects the underlying metallic surface from degradation. The endoprosthesis may be of the type that is radially expandable between a generally unexpanded insertion circumference and an expanded implantation circumference which is greater than the unexpanded insertion circumference. When the endoprosthesis is of a type having an underlying substrate with a relatively large surface area, the carbon coating can be especially useful in maintaining patency.
Endoprostheses are known for treating stenoses, stricture, aneurysm conditions and the like. An endoprosthesis device of this type, which is at times referred to as a stent, is typically placed or implanted by a mechanical transluminal procedure. Often a device of this type is percutaneously implanted within the vascular system to reinforce collapsing, partially occluded, weakened and/or abnormally dilated localized sections of a blood vessel or the like. Stents of this general type can also be used in the urinary tract, the bial tract, the intestinal tract and the like. When endoprostheses or stents are used to treat a stenosis condition, typically such is done in association with a dilation element such as an angioplasty balloon. In this situation, the dilation element or balloon device opens the constriction, and the stent or the like is positioned thereat in order to prevent or at least substantially slow re-formation of the stenosis.
Generally speaking, currently available conventional stents present an implantation interface that is smooth and generally rigid, often being made of stainless steel or other metal. Typically, these structures present an implantation interface that is inherently thrombogenic. After implantation, loosely adhered tissue will surround such conventional stents or tubular endoprostheses, and this loose tissue will be constantly traumatized by motion of the blood vessel wall. Besides presenting a generally thrombogenic surface, stents of this type are typically constructed of wire materials that can degrade during extended implantation periods.
Another attribute of many stents is that they are radially compressible and expandable so they will easily pass through blood vessels or the like when they are collapsed and will expand to an implanted size after the stenosis, aneurysm or the like has been reached. It is also generally desirable that a stent be substantially flexible throughout its length so that it is easily maneuverable through bends and curves of the blood vessel or the like. These desirable flexibility and maneuverability attributes can themselves lead to potential problems. Relative motion between the surface of the stent and the vessel or the like within which it is implanted can lead to trauma of the blood vessel and/or can contribute to conditions under which a portion of a stent, particularly one including thin wire components, may fracture.
Currently known stent products have a variety of different structures. Included are those which are essentially coiled springs. When this type of spring stent is tightly coiled, its diameter is relatively small for insertion through a blood vessel or the like. When the coil is sprung or coiled more loosely, the stent assumes its expanded, implantation orientation. Maass et al U.S. Pat. No. 4,553,545 is illustrative of this type of coiled spring stent or endoprosthesis. Multihelix or braided stents are also known. Palmaz U.S. Pat. No. 4,733,665 is representative of an expandable stent of this general type. Gianturco U.S. Pat. No. 4,580,568 illustrates a percutaneous endovascular stent formed of stainless steel wire that is arranged in a closed zig-zag pattern. Another type of stent is known as a Statz stent, and it includes a hypodermic tube with longitudinal slots etched into its body.
The respective implantation interfaces that are provided by these typical types of stent structures are usually generally smooth metallic surfaces. With some of these structures, the metallic surface is provided in the form of thin wires that can be relatively widely spaced apart. While stents of this general type have many advantageous properties, particularly from the point of view of their flexibility and maneuverability, they can present a situation in which the stent has an implantation interface that includes relatively widely spaced longitudinal edges of thin and smooth metal wires. It is, of course, important to minimize potential trauma that can develop during long term implantation of these types of devices.
The present invention retains most of the advantageous features of the various stents or tubular endoprostheses such as those discussed herein. At the same time, various deficiencies of these types of structures are avoided, while important and advantageous features are realized In summary, the generally tubular endoprosthesis of this invention includes a generally cylindrical metallic body member having a pyrolytic amorphous carbon layer on at least the outwardly facing surface thereof. When desired, the generally cylindrical metallic body member has a porous surface, and a porous carbon surface is defined when pyrolytic amorphous carbon is coated thereover.
It is a general object of the present invention to provide an improved generally tubular endoprosthesis.
Another object of the present invention is to provide an improved endoprosthesis or stent having an amorphous carbon layer on at least its outer surface.
Another object of the present invention is to provide an improved endoprosthesis or stent which has an outside surface of carbon coated over a porous substrate to thereby present a porous interface during implantation.
Another object of this invention is to provide an improved endoprosthesis or stent that has enhanced antithrombogenic properties.
Another object of this invention is to provide an improved endoprosthesis or stent that is protected from degradation upon implantation.
Another object of the present invention is to provide a improved carbon-coated endoprosthesis for transluminal implantation and that has very large radial expansion capabilities.
Another object of this invention is to provide an improved endoprosthesis or stent which is radially expandable by an expanding member or balloon of a catheter device.
These and other objects, features and advantages of this invention will be clearly understood through a consideration of the following detailed description.